AKT. 15 THE FOSSIL CRIiSTOID GENUS VASOCRINUS KIEK 9 



Height of RK (average), 6 mm. 

 Breadth of RR (average), 13 mm. 

 Breadth of arm facet (average), 6.5 mm. 



Specimen 3& gives the following measurements : 



Height of cup, 9 mm. 



Diameter of cup (aut. to post. IR), 15.5 mm. 



Diameter of stem, 4.6 mm. 



Pleight of IBB, 1.6 mm. 



Height of BB, 4.7 mm. 



Breadth of BB (average), 6 mm. 



Height of RR (average), 4.5 mm. 



Breadth of RR (average), 7.3 mm. 



Breadth of arm facet (average), 4.3 mm. 



It will be seen that the dorsal cup is low, with a breadth consider- 

 ably in excess of the height. The infrabasals form a sharply defined 

 ring with nearly vertical walls. Above, the sides of the cup diverge 

 gently to about one-half the height of the basals. At this point the 

 sides of the cup flare outward abruptly to give the maximum diam- 

 eter of the cup at the lower margins of the arm facets. This form 

 of the dorsal cup is characteristic of adult individuals. In the case 

 of two large specimens that show the profile of the cup, other than 

 speciman da from which the description given above was made, there 

 is a slight variation in the outline as given. In one specimen the cup 

 is relatively lower. The infrabasal ring is less sharply defined, and 

 the abrupt outward flare of the sides of the cup involves the greater 

 part of the basals. In another specimen where the surface contours 

 of the plates are better preserved than in the case of the type the 

 outward flare appears to be somewhat less pronounced when the basals 

 are viewed in profile, owing to the relatively high relief of the plates. 

 As a matter of fact, the shape of the cup is about like that of the type. 

 In specimen 36, which is a much younger specimen, the relative pro- 

 portions of height to breadth are almost exactly the same. Here, 

 however, instead of the abrupt outward flare of the walls of the cup, 

 the sides diverge more evenly from the top of the infrabasal ring. 



The stem, judged by its impression on the infrabasals, was large, 

 round in section, and traversed by a large pentagonal or obscurely 

 pentalobate lumen. A dissociated fragment of column placed by 

 Lyon with his specimens of VasocHnus is pentagonal in section, with 

 rounded angles. The lumen of this fragment, its size, and the char- 

 acter of the striae on the faces of the columnals are all very like the 

 impressions of the proximal columnal as shown 6n the infrabasals. 

 It may be, therefore, that the column was pentagonal in cross-section. 



The infrabasals are subequal in size and together form a well- 

 defined cylindrical ring or collar. The lower outer margins of the 

 infrabasals are somewhat thickened, forming a rounded ridge. The 

 basals are irregularly unequal in size. All except those adjacent to 



